There has been a lot of news coverage lately about disruptions to train services through the Eurotunnel and particularly the impact this has had on Eurostar services.
Eurostar have a Service Disruption status page which gives the current status of services they are offering and any additional news for passengers who have already booked when there are issues and what they can do to reschedule their trip if required.
If you have not booked a trip and are considering your options then it is worth taking a look at P&O Ferries Dover to Calais Offers Page.